changed 'the_end' to '999_the_end'

build.zig

@@ -461,7 +461,7 @@ const exercises = [_]Exercise{
     //     .@"async" = true,
     // },
     .{
-        .main_file = "the_end.zig",
+        .main_file = "999_the_end.zig",
         .output = "This is the end for now!\nWe hope you had fun and were able to learn a lot, so visit us again when the next exercises are available.",
     },
 };